Directional radio beacon



Jian. l, 1943. A. H. HERMANSSON v I25309136@ DIRECTIONL RADIO BEACON Filed DSC. 11, 1940 2 Sheets-511932 1 IVVENTOR MQ/Q mm EY f ATTORNEY' M l, 1943.. A. H. HERMANSSON DIRECTIONAL RADIO BEACON V Filed Deo. i1, 1940 2 sheets-sheet' 2 MZ M EY `high directional sharpness.

Patented Jan. 19, 1943 UN ITE.

TES

ATENT -QFFICE assignor to Aga-Baltic Radio Aktiebo'lag,

Stockholm, Sweden, a corporation of Sweden Application 'December 11, 1940, serial No. 369,579

In Sweden January 4, 1940 6 claims. lol. 25o-11) My invention relates to directional radio beacons.

Directional radio beacons are known in which the direction of transmission is reversed in a predetermined sequence, usually either in time with the code letters e and t or a. and 1t or sometimes in time with other code letters. A listener on one side of a certain plane through the radio beacon will only hear the letter e (or a) whereas a listener on the other side of this plane will only hear the letter t (or n). If the listener passes from one side of the plane to the other, he will pass a certain position, namely, the said plane where both signals are heard with equal intensity. As these signals were formed by shifting the phase characteristic of the directional beacon, the signals will complete each other so that a continuous tone is heard, indicating that the listener is in the desired plane.

These radio beacons are usually called E-T- beacons. The directional sharpness is as a rule very good with such radio beacons and for this reason they are growing to be used more and more for indicating courses on land, on sea or in the air. Although the E-T-beacons offer a relatively high directional sharpness they have also certain disadvantages. Especially prominent is the diiiiculty of building phase shifting apparatus with sufficient precision. Phase shifters used hitherto have as a rule been rather complicated and it was necessary to make them of rather high precision in order to obtain the These circumstances have substantially retarded the commercial use appearance of E-T-beacons.

In the drawings:

Fig. 1 is a diagrammatic view of a directional radio beacon embodying the present invention;

Fig. 2 is a plan diagram illustrating the operation of the beacon of Fig. 1;

Fig. 3 is a plan View of a phase shifting condenser illustrating a known form thereof;

Fig. 4 is a diagram illustrating the operation of the condenser of Fig. 3;

Fig. 5 is a diagram illustrating the operation of the phase shifting condensers embodying the present invention; and

Figs. 6 and 7 are plan views of phase shifting condensers embodying the present invention and operating in accordance with the diagram of Fig. 5. Y

Fig. 1 of the annexed drawings shows a known type of E-T-beacons. The transmitter is indicated II. This is connected over a phase shifter I2 to a loop antenna I3 and through a transformer [Il to a non-directional antenna I5. The phase shifter contains a set of condenser plates which are actuated by a code mechanism I6 in time with the code letters e and t.

The operation of the arrangement is evident from Fig. 2, in which the characteristic of the non-directional antenna is indicated at I'I and the characteristic of the directional antenna at I8. Both of the characteristics combine to produce a directional characteristic I9. It may be assumed that the part of the characteristic IS drawn in full'lines is in phase with the characteristic il, whereas the part of the characteristic I8 drawn in dot and dash lines is in counter-phase. By shifting of the phase of the current in the loop antenna I3 the phase of the characteristic IB will be shifted, and as a consequence thereof the resultant combined characteristic is shifted by 180 as indicated at 20.

If the phase shifting takes place in time with the code letters e and t which complete each other a listener in the direction ZI from the beacon Will hear the letters e with an intensity represented by the point 22 in the diagram, and the letters t with an intensity represented by the point 23 in the diagram. If the listener moves to the direction 24 in relation to the diagram he will obviously hear the letters e and t with the same intensity as represented by the point 25 in the diagram.

In systems of this kind the listener tries to iind a direction in which a continuous tone is heard. However, the switching over of the phase shifter from one position to the other takes a certain time during which the sound intensity is changed, thereby producing a very disturbing effect, or a phase-shifting click, which is particularly noticeable as the direction 24 is approached where the difference between the two sound intensities is small.

An object of the present invention is to decrease the phase shifting click to a minimum for the purpose of making possible a higher precision in observation. The invention is based on the discovery that the intensity of the click is directly proportional to the second derivative of the change of capacity in the phase shifter. Hitherto the condenser plates of the phase shifters were made as shown in Fig. 3. The stator part contained plates 26, 21 of relatively great angular extension, viz. approximately separated by a relatively small interspace 28, whereas the rotor contained rectangular plates 29. The radial edges of the stator and of the rotor were straight lines. The capacity of the rotor 29 t0 the stator plate 26 is maximum during the rather wide angle of turning, during which the rotor plate 29 is wholly between two adjacent stator plates, whereas the capacity begins to decrease abruptly when the rotor plate 29 begins to shift to the interspace 28. The capacity curve thus changes abruptly at this point. From this point until the rotor plate 29 leaves the interspace 28 the capacity changes according to a substantially linear curve, and at this last named point the curve again changes abruptly.

The curve is sh wn in Fig. Ll, in which the curve 36 represents the capacity between the rotor plate 29 and the stator plates 26, whereas the curve 3l represents the capacity between the rotor plate 29 and the stator plates 2l. 32 is the point of abrupt change, arising when the rotor` plate 29 begins to enter the opening 28, and 33 is the point of abrupt change occurring when the rotor plate 29 registers with the stator plates 2l. According to this invention the rotor plate or possibly the stator plates are given such a form that a transition is obtained which is free from abrupt changes, this form preferably being equal to the form of the second and third quarter of a period of a sine curve. Fig. shows graphically the course of the change of capacity according to this invention. The curve 34 represents the capacity between the rotor plate 29 and the stator plates 26, whereas the curve 35 represents the capacity between the rotor plate 29 and the stator plates 2l. The curve 36 shows the difference of capacity and consequently, the amplitude of the wave transmitted from the loop antenna I3. It is evident from Fig. 5 that the phase shifting follows a fully continuous curve 36 whereby the phase shifting clicks are brought down to a minimum.

Fig. 6 shows a form of rotor plate according to the invention. The stator plates 2S and 2l are arranged as in Fig. 3, but the rotor plate 29 is formed about double the width of the plate 29 in Fig. 3, and with an outline shaped to produce the phase shifting characteristic shown in Fig. 5.

It is desirable to make phase Shifters as light as possible because they are not always kept in continuous rotation at a constant speed, but in order to shorten the phase shifting interval may oscillate or possibly rotate at variable speeds. The less the mass of the rotating parts, the higher the precision that can be obtained.

The mass of the movable part is determined by the necessary capacity surface of the plates 29, and this is determined by the spacing between the stator and rotor plates. This spacing should accordingly be made as small as the precision of adjustment permits.

In the arrangement according to Fig. 6, however, the rotor plate 29 begins its exit from the air interspace between the stator plates 2S at a point represented at 37 in Fig. 5. One moment later on the rotor plate 29 begins to enter between the stator plates 21. A phase displacement is thus present between the two curves 34 and 35, which is not desirable. This phase displacement is directly proportional to the width of the space 28, and for avoiding the phase displacement the space 28 should be made iniinitely small, which for practical reasons is possible. 4

Fig. 7 shows an arrangement by which these disadvantages are avoided. In the arrangement according to Fig. 7 the stator plates are given a span of exactly one eighth of one revolution and equally spaced. On the other hand the rotor exactly the same speed as that with which the capacity of the wing 2U to the stator plates 2l increases between the points 38 and 39. The total capacity between the wings 4:) and ii and the stator plates 2l will thus be constant up to the point 39 where the wing 1H leaves the stator plates 27 and begins to enter between the stator plates ft2. rThe wing 40 then begins to leave the interspace between the stator plates 2l, so that the capacity of the rotor to these stator plates decreases.

Disregarding the possible edge capacities, the form of the wings 29, @il and il which gives to the phase shifting the sine characteristic shown in Fig. 5, is obtained by laying out in radial direction from the inner periphery of the plates 26, 21 distances which are determined as a sine function of four times the radial angles of the respective points. This is of course correct on the assumption that two rotor plates and Iour stator plates are used. If the number of rotor and stator plates is diierent the angle must be adapted in a corresponding manner.

If an arrangement according to Fig. 6 or 7 is in continuous rotation the phase shifting period 37-38 will be too long as compared with the signal period 38-39, whether this signal period represents the letter e or the letter t. This disadvantage may be avoided by varying the movement of the rotor in a suitable manner. For instance the rotor may rotate with varying speeds, so that the speed is lower during the period 38-39 than during the period 31-38. It is also possible to arrange the phase shifter so that it moves discontinuously, the phase shifter being stationary during a suitable interval of time within the period 228-39, or the phase shifter may oscillate with some suitable characteristic between the two periods of constant output amplitude on opposite sides of the phase shifting period 31-38. There are also other manners in which this problem may be solved. The manner of solving this special problem has, however, nothing to do with the present invention.

The invention is of course not limited to the particular embodiments shown and described which may be modiiied in various ways without departing from the scope of the invention. Thus it is possible to deviate somewhat from the ideal sine form of characteristic during the phase shifting. It is essential, however, that the phase shifting take place without discontinuity.

What is claimed:

l. A directional radio beacon comprising a directional transmitter and a phase shifting means connected to periodically reverse the direction of transmission of said transmitter, said phase shifting means comprising sets of stator and rotor plates connected to form a phase shifting condenser, one of said sets of plates having leading and trailing edges curved in the direction of rotation in a manner to avoid abrupt capacity changes as the rotor plates enter or leave capacity registration with the stator plates.

2. A directional radio beacon comprising a directional transmitter and a phase shifting means connected to periodically reverse the direction of transmission of said transmitter, said phase shifting means comprising sets of stator and rotor plates connected to form a phase shifting condenser, one of said sets of plates having leading and trailing edges curved in the direction of rotation in a manner to produce a changeover capacity characteristic represented by the second and third quarters of a sine wave as the rotor plates enter or leave capacity registration With the stator plates.

3. A directional radio beacon comprising a directional transmitter and a phase shifting means connected to periodically reverse the direction of transmission of said transmitter, said phase shifting means comprising stator and rotor plates connected to form a phase shifting condenser, said stator plates each extending over a radial angle of about 180 divided by the number of rotor plates and being arranged in the same plane, the rotor plates each extending over a radial angle substantially equal to the angular extension of each stator plate and having leading and trailing edges curved in the direction of rotation in a manner to avoid abrupt capacity changes as the rotor plates enter or leave capacity registration with the stator plates.

4. A directional radio beacon comprising a directional transmitter and a phase shifting means connected to periodically reverse the direction of transmission of said transmitter, said phase shifting means comprising stator and rotor plates connected to form a phase shifting condenser, said stator plates being of segmental form and arranged in the same plane, said rotor plates Cil each comprising a pair of adjacent wings which extend over about the same radial angle as each stator plate, the leading and trailing edges of said rotor plates being curved in the direction of rotation in a manner such that during the changeover period the decrease of capacity between one stator plate and the trailing portion of the rotor plate is substantially equal to the increase in capacity between the next stator plate and the leading portion of the rotor plate, whereby abrupt capacity changes are avoided.

5. A directional radio beacon comprising a directional transmitter and a phase shifting means connected to periodically reverse the direction of transmission of said transmitter, said phase shifting means comprising stator and rotor plates connected to form a phase shifting condenser, said rotor plates having leading and trailing edges curved in the direction of rotation in a manner to avoid abrupt capacity changes as the rotor plates enter or leave capacity registration with the stator plates.

6. A directiona1 radio beacon comprising a directional transmitter and a phase shifting means connected to periodically reverse the direction of transmission of said transmitter, said phase shifting means comprising stator and rotor plates connected to form a phase shifting con- 

